Liver shunt in dogs is a serious, life threatening disease and one of the most important inherited Miniature Schnauzer health problems.
Other names for the this condition are: hepatic shunt, portosystemic shunt and portovenal shunt.
What is a Liver Shunt?
In a normal mammal such as the dog, the liver has the job of processing nutrients taken up from the intestine.
A big part of its work is processing and detoxifying proteins that in their original form can damage the central nervous system, rendering them harmless and able to be utilized by the body to build its own tissue.
A liver shunt is simply a vein (or sometimes several veins) that effectively bypass the liver and deliver these toxins straight into the bloodstream unprocessed.
So, What Causes It?
In the normal mammal embryo the liver is not mature enough to take on the job of detoxifying nutrients – this work is done by the liver of its mother.
Near birth these embryonic blood vessels normally shut down to allow the adult veins from the intestines to the liver to take over.
However, in some puppies they fail to shut down, and the puppy is born with a congenital liver shunt.
The vein(s) that make up the liver shunt in dogs can be either buried inside the liver (intrahepatic) or form outside of the liver (extrahepatic).
Intrahepatic shunts are much harder to correct surgically and tend to affect large breed dogs including Irish Setters, Irish Wolfhounds, German Shepherds, Golden Retrievers, and Samoyeds.
Extrahepatic shunts are much easier to deal with surgically and are most commonly seen in smaller breeds such as the Dachshund, Lhaso Apso, Maltese, Miniature Schnauzer, Pekingese, Poodle, Pug, Shih Tzu and Yorkshire Terrier.
What are the Signs of a Liver Shunt?
As puppies are born with the disorder, signs usually develop in the first six months of life, and almost always by the time the dog is two years old.
The puppy will often appear completely normal in the first few months of its life, though perhaps be a bit quieter than its litter mates and small for its age.
Over time, intermittent signs may develop. These will often come and go and be preceded by a high protein meal.
• Lethargy and weakness
• Occasional vomiting and diarrhea
• Excessive drinking and peeing
• Because kidney stones sometimes develop, there may be difficulty peeing and perhaps blood in the urine
• Due to toxins reaching the brain, central nervous symptoms will be become apparent including changes in behavior, disorientation, confusion, seizures or convulsions, circling, pacing, head pressing and even blindness.
Eventually the pup lapses into a coma and dies…
Is There Any Treatment?
Owners of puppies with a liver shunt face an alarming round of very expensive blood tests, Xrays and other procedures before it can even be properly diagnosed.
The only treatment is surgery, which is most likely to succeed in dogs with the extrahepatic shunt.
Low or no-protein diets are mandatory ever after to reduce the load on the stressed out liver, and allow the dog to enjoy something approaching reasonable health.
However, even after “successful” surgery affected dogs are never really vibrantly healthy again.
Is it the Breeder’s Fault?
Hepatic shunts are not well understood yet, but do tend to run in particular family lines, implying that they can be inherited. In these cases, a responsible breeder would stop using affected dogs for breeding.
However, they can also appear spontaneously (but rarely) in pups from families with no history of the disorder. Sometimes God makes a mistake! In these cases it’s simply a case of rotten luck for the poor owners.
Though some people say that a dedicated breeder should be able to recognize that “something is not quite right” in congenital liver shunt puppies before they go to their new owners (i.e. in the first 8 weeks of life) in my experience this is not the case.
As a veterinarian with 18 years of breeding Miniature Schnauzers this problem has occurred once in a puppy I bred, and was certainly not at all apparent until the puppy was several months old and out of my care.
And if you are unfortunate enough to buy a puppy that turns out to be affected, your breeder should at least reimburse you the cost of the puppy or offer to replace it for you.
How can I avoid it?
Aside from noticing that their dogs are producing affected puppies, breeders can’t yet screen for this condition.
Go for outbred rather than inbred or line bred dogs! See the discussion of this important issue on the Miniature Schnauzer health problems – PRA page.